A. Field of the Invention
This invention relates to the manufacture of mass customized items, and more particularly to automated manufacturing processes of the same.
B. Description of the Related Art
Traditional methods of dental mold making are well known, and include such methods and apparatuses as are described in U.S. Pat. No. 6,497,574, assigned to the assignee of the present application and incorporated by reference herein its entirety.
In such systems, a dental “aligner”, for application to a patient's teeth, is made from a mold. A series of aligners is constructed which are sequentially applied by the patient to their teeth and which result over time in beneficial changes to the patient's dental structure. The initial mold is made from an impression of the patient's teeth and the subsequent molds and aligners are made using software and a digitization of the initial mold. As described in the patent incorporated by reference above, the initial mold may be constructed by forming an impression of the patent's dentition using a suitable impression material, such as alginate or polyvinylsiloxane (PVS). Impressions of the upper jaw typically include the teeth, the palate and gingival tissue surrounding the teeth on the facial and lingual surfaces. Impressions of the lower jaw typically include the teeth and gingival tissue surrounding the teeth on the facial and lingual surfaces. Plaster is then poured into the impression to form a relief of the dental features. The relief is a permanent, three-dimensional mold of the dentition and oral tissues.
Improved methods of mold making include rapid prototyping. Rapid prototyping is a technology that has developed in the last decade. Through the use of modem solid modeling CAD packages, combined with laser systems and new materials, solid parts may now be generated directly from a computer model. Examples of this technology include stereolithography (SLA), laminate object manufacturing (LOM), and fused deposition modeling (FDM), to name a few.
Stereolithography is a method that employs an ultraviolet laser to cure a thin layer of liquid plastic into a solid. The process operates by taking a thin layer of the light-sensitive liquid plastic and passing the laser beam over the points where the part is solid. Once a pass is completed, another layer of the liquid is added to the existing part, and the process repeats until the full part height is achieved. SLA parts are extremely accurate, and tend to have excellent surface finishes. A variety of SLA materials are available for different purposes, including waxes, plastics, and flexible elastomers. Typically, an SLA process may produce some 20-25 molds in an hour.
Producing a dental mold with rapid prototyping methods requires the use of a computerized model or digital data set representing the dental geometry and tooth configuration. The model is used to guide the mold making process to produce a replica or relief of the computerized model. The resulting relief is a three-dimensional mold of the dentition. This method of making dental molds is particularly applicable to situations in which multiple molds must be produced. In this case, one computerized model may be used to make a number of molds in an automated fashion. In addition, this method is applicable to situations in which a mold of a tooth arrangement that differs from the patient's current tooth arrangement is needed to be produced or molds of multiple tooth arrangements that differ from each other and the patient need to be produced. In either case, the computerized model of the patient's teeth may be manipulated to portray each new tooth arrangement and a mold may be produced to reflect each successive arrangement. This may be repeated any number of times to derive a number of molds with differing tooth arrangements. Such techniques may speed production time and reduce costs by eliminating the need for repeated casting and artistic resetting of teeth in traditional mold manufacturing.
Series of dental molds, such as those described above, may be used in the generation of elastic repositioning appliances for a new type of orthodontic treatment being developed by Align Technology, Inc., Santa Clara, Calif., assignee of the present application. Such appliances are generated by thermoforming a thin sheet of elastic material over a mold of a desired tooth arrangement to form a shell. The shell of the desired tooth arrangement generally conforms to a patient's teeth but is slightly out of alignment with the initial tooth configuration. Placement of the elastic positioner over the teeth applies controlled forces in specific locations to gradually move the teeth into the desired configuration. Repetition of this process with successive appliances comprising new configurations eventually moves the teeth through a series of intermediate configurations to a final desired configuration. For example, a new appliance with a slightly different configuration may be worn for 20 days before replacement with the next appliance in the sequence. A full description of an exemplary elastic polymeric positioning appliance is described in U.S. Pat. No. 5,975,893, and in published PCT application WO 98/58596 which designates the United States and which is assigned to the assignee of the present invention. Both documents are incorporated by reference for all purposes.
To carry out such orthodontic treatment, a series of computer models or digital data sets is generated, stored and utilized to fabricate a series of representative dental molds. The fabrication of a series of aligners from such a series of molds involves disposing the molds in a thermoplastic fabrication machine to produce each aligner. The fabrication machine usually relies on selectively hardening a non-hardened resin to produce the appliance or aligner. This fabrication of a series of aligners from such a series of molds requires a significant amount of labor because each mold must be individually hand-inserted and manipulated in the thermoplastic fabrication machine to produce each aligner. This laborious process is operator-intensive and slow as generally only a single workpiece may be fabricated at a time. Other mass-customized manufacturing process are similarly labor-intensive.